In this situation, whichever function sub was imported
last will be called. If you have warnings enabled, you will get a warning when importing a
function that has already been defined/imported; you won't get
such a warning w/ a variable (at least I don't think you will).

This is why you have to be careful when writing modules that
export; you can easily trample someone else's namespace. Which
is part of the reason why module authors are encouraged to
use @EXPORT_OK instead of @EXPORT; you give the user of your
module the choice of which functions/variables he/she imports,
plus you make it very explicit to any reader of your code (including
you :) which functions and variables you're importing. Ie. you
can look at the use line and *know* what you're importing
into your namespace.